Local Modification of Speed of Sound in Lithium Alumino-Silicate Glass/Ceramic Material by Pulsed Laser Irradiation and Thermal Processing

Abstract

Glass and glass/ceramics are now used in modern devices with increasing frequency. A list of the notable material properties commonly will not include a capability to guide ultrasonic waves. The photosensitive glass ceramics (PSGCs), an old invention with recent technological rebirth, may enable this capability. The speed of sound (SoS) has been measured at an ultrasonic frequency (75 MHz) in a commercially available PSGC material. The measurements are made using a pulse echo time-of-flight (TOF) technique as a function of UV laser exposure and thermal processing. The measured increase in the SoS correlates with the density of crystalline matter present, which can be metered by controlling the exposure dose. For the Li2SiO3 crystalline phase, the results show the shear (transverse) wave mode velocity can be increased by 4.8% relative to an unexposed area where no crystalline matter exists. The maximum change in velocity for the longitudinal (compressional) wave mode is only 2%. However, by altering the thermal processing protocols to grow the high temperature Li2Si2O5 crystalline phase, the measured change in the SoS increases to 11% and 9%, respectively. These results permit the volumetric patterning of delay lines by laser direct write techniques for generating complex profile ultrasonic wave patterns. Moreover, by patterned 3D shaping (i.e., photostructuring), ultrasound energy can be harnessed and utilized to advantage.